Abstract
This study analyzes two wind-induced upwelling mechanisms, namely, Ekman transport and Ekman pumping that occur during the southwest monsoon. The results suggest that the coastline of the east coast of Peninsular Malaysia (ECPM) is affected by upwelling with spatiotemporal variations. Characterization of upwelling by using wind-induced upwelling indexes (UIW) indicate the existence of favorable upwelling conditions from May to September. Upwelling intensity increased in May and peaked in August before declining in September, decreasing intensity from the southern tip towards the northern tip along the coastline of the ECPM. The existence of upwelling along the ECPM has resulted in an important difference between the SSTs of the inshore and the oceanic regions. Nonetheless, the use of the SST gradient between the inshore and the oceanic SSTs to characterize upwelling (UISST) was found to be unsuitable because the SST along the ECPM was affected by water advection from the Java Sea and incessant changes in the SST. In order to indicate the major contributor of wind-induced upwelling along the ECPM in terms of the spatiotemporal scale, a comparison between Ekman transport and Ekman pumping was drawn by integrating Ekman pumping with respect to the distance where the positive wind stress curl existed. The estimation of Ekman transport and Ekman pumping indicated that Ekman pumping played a major role in contributing towards upwelling in any particular month during the southwest monsoon along the entire coastline of the ECPM as compared to Ekman transport, which contributed towards more than half of the total upwelling transport. By dividing the ECPM into three coastal sections, we observed that Ekman pumping was relatively predominant in the middle and northern coasts, whereas both Ekman transport and Ekman pumping were equally prevalent in the southern coast.
Highlights
Upwelling has been traditionally described as a process that significantly affects the primary productivity and fishery production because it involves the wind-driven motion of cooler and nutrient-rich water from the deeper ocean layers to the surface, thereby replacing the nutrientdepleted surface water [1,2]
The results suggest that the coastline of the east coast of Peninsular Malaysia (ECPM) is affected by upwelling with spatiotemporal variations
The south to southwesterly winds were dominated by the meridional component that prevailed over the southwestern part of the South China Sea (SCS); these winds ran alongshore, roughly parallel to the coastline along the southern and middle coasts, and almost in a perpendicular direction, which was directed offshore along the northern coast of the ECPM
Summary
Upwelling has been traditionally described as a process that significantly affects the primary productivity and fishery production because it involves the wind-driven motion of cooler and nutrient-rich water from the deeper ocean layers to the surface, thereby replacing the nutrientdepleted surface water [1,2]. In the case of Ekman transport, the alongshore prevailing winds exert a uniform Coriolis force to drive the surface water either offshore or onshore, which in turn pushes the deeper coastal water upward or downward. The Ekman transport component perpendicular to the coastline and Ekman pumping have been commonly used for characterizing upwelling (hereafter referred to as the wind upwelling index, UIW). In addition to Ekman transport and Ekman pumping, some authors have considered the sea surface temperature (SST) gradient between the coastal water and oceanic water as an alternative parameter to characterize upwelling (hereafter referred to as the SST upwelling index, UISST) [9,10,11,12,13,14]. With regard to UISST, the temperature differences between the coastal water and the oceanic water cannot be directly attributed to upwelling because the water temperature is affected by local and large-scale external factors, such as freshwater input, large-scale atmospheric phenomena, and synoptic-scale weather and climate systems [9,12]
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